Draft White Paper 

REVIEW OF “THORIUM IN-VIVO COWORKER STUDY FOR FEMP – 

A PROPOSED ATTACHMENT FOR ORAUT-TKBS-0017-5, REV. 1” 

Contract Number 200-2009-28555 

Prepared by 

S. Cohen & Associates 

1608 Spring Hill Road, Suite 400 

Vienna, Virginia 22182 

Saliant, Inc. 

5579 Catholic Church Road 

Jefferson, Maryland 21755 

June 2010 

Disclaimer 

This document is made available in accordance with the unanimous desire of the Advisory Board on 

Radiation and Worker Health (ABRWH) to maintain all possible openness in its deliberations. However, 

the ABRWH and its contractor, SC&A, caution the reader that at the time of its release, this report is predecisional and has not been reviewed by the Board for factual accuracy or applicability within the 

requirements of 42 CFR 82. This implies that once reviewed by the ABRWH, the Board’s position may 

differ from the report’s conclusions. Thus, the reader should be cautioned that this report is for 

information only and that premature interpretations regarding its conclusions are unwarranted.
TABLE OF CONTENTS 

Introduction......................................................................................................................................5 

Summary of ORAUT White Paper......................................................................................5 

1.0 Summary of Findings...........................................................................................................8 

2.0 SC&A Review Comments – General Comment 1.............................................................11 

2.1 Uncertainty in Interpretation of Data for the Period 1968–1978...........................11 

2.2 Consistency of Pre-1979 and Later In-vivo Thorium Data ...................................13 

2.3 Apparently High Imprecision in Pre-1979 In-vivo Thorium Measurements.........15 

2.4

.................16 

Incompatibility of Fernald In-vivo Thorium Data Recorded as mg of 

Thorium with the MDA for Th-232 Given in ORAUT-TKBS-0017-5

2.5 Lack of Information on the MIVRCL System and Calibration for Pb-212...........16 

2.6

.....................................................................................16 

Lack of Information on the MDA and Uncertainties on the Significance of 

the In-vivo Pb-212 Results

2.7

........................................................................................................................17 

Equilibrium, Activity Ratios, and Interpretation of Pb-212 Results, 1978–

1988

2.8 Possible Overestimates of Background for Pb-212 ...............................................19 

3.0 SC&A Review Comments – General Comment 2.............................................................20 

3.1 Identification of Thorium Production Workers and Associated Data ...................20 

3.1.1 Starkey Memo............................................................................................21 

3.1.2 Thorium Workers Identified by Individual In-vivo Logsheets..................23 

3.2 In-vivo Monitoring by Plant During Thorium Production Periods .......................26 

3.3

................................................................................................................31 

Episodic Exposure Potential Involving the Redrumming of Thorium 

Materials

3.4 Feasibility of Identifying Additional Thorium Workers........................................33 

3.5 Potential Inadvertent Exposure to Non-Thorium Workers....................................34 

References......................................................................................................................................36 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.
LIST OF FIGURES 

Figure 1: In-vivo Data for a Fernald Worker, Recorded as mg of Thorium..............................12 

Figure 2: In-vivo Data for a Fernald Worker, Recorded as mg of Thorium..............................12 

Figure 3:

...........................................................................................13 

Example of In-vivo Data for a Fernald Worker showing a Reasonably 

Continuous Transition of pre-1979 In-vivo Measurements with Later 

Measurements, using the Conversion Factor 1 mg Th = 0.11 nCi for pre-1979 

Data Proposed by NIOSH

Figure 4:

...................................................................................14 

In-vivo Data for a Fernald Worker for whom pre-1979 Data Clearly 

Do Not Merge with Later Data

Figure 5:

...................................15 

Data for a Thorium Worker Illustrating the Typically Higher Variability of Invivo Thorium Measurements Recorded as mg of Thorium than of Later 

Measurements Recorded as Activities of Ac-228 and Pb-212

Figure 6.

..............................................................................18 

Activity Ratio Th-232:Pb-212 in Lungs of Rats as a Function of Time 

after Intratracheal Instillation of Different Masses of Th-232 + Th-228 

as Thorium Dioxide or Hydroxide

Figure 7.

...................................................................................18 

Activity Ratio Th-232:Pb-212 in Lungs of Rats as a Function of Time after 

Intratracheal Instillation of Different Masses of Th-232 + Th-228 

as Thorium Nitrate or Fluoride

Figure 8.

........................................................................................19 

Example of a Thorium Worker for Whom Nearly All In-vivo Pb-212 

Measurements are Negative

Figure 9.

........................................................................................19 

Example of a Thorium Worker for Whom Nearly All In-vivo Pb-212 

Measurements are Negative

Figure 10.

......................................................................21 

For the ‘60 Th workers’ Identified by SC&A, the Number Employed by Year 

and the Percentage Monitored by Year

Figure 11.

............................................................................................................................22 

Rank Ordered 1968 Thorium Lung Burden (in mg Th) for 51 Thorium 

Workers Identified in Starkey Memo Compared to All Monitored Workers in 

1968

Figure 12.

......................................24 

Rank Ordered In-vivo Results (mg of Th) for All Monitored Workers and 

Thorium Workers (at both Thorium Production Facilities and Non-production 

Facilities) for the Thorium Production Period (1968–1979)

Figure 13.

......................................24 

Rank Ordered In-vivo Results (mg of Th) for All Monitored Workers and 

Thorium Workers (at both Thorium Production Facilities and Non-production 

Facilities) for the Thorium Production Period (1968–1979)

Figure 14.

................................25 

In-vivo Results in mg of Thorium for 9 “Thorium Workers” and 17 “Former 

Thorium Workers” as Identified by Their Individual Logbooks

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Health for factual accuracy or applicability within the requirements of 42 CFR 82.

NOTICE:

Figure 15.

...........................................................................................26 

Comparison of In-vivo Data in mg of Thorium from the Identified “Thorium 

Workers” and “Former Thorium Workers” with All In-vivo Results Found in 

NIOSH’s Excel Database

Figure 16. Percentage of the Total In-vivo Thorium Samples by Plant for the Year ..................30 
INTRODUCTION 

During the Fernald Work Group meeting held on January 29, 2010, SC&A identified and the 

work group discussed six issues. Issue 6 is concerned with National Institute for Occupational 

Safety and Health’s (NIOSH’s) approach for reconstructing the doses to workers exposed to 

Th-232. This issue has two parts. The first part deals with pre-1968 breathing zone (BZ) 

samples and the degree to which that data can be used to reconstruct worker internal exposures to 

Th-232. SC&A had previously provided NIOSH with a detailed report regarding our findings on 

this matter, and there had been a considerable amount of material and reports exchanged between 

NIOSH and SC&A prior to the January 29, 2010, meeting. During that meeting, John Stiver 

(SC&A) provided a recap of the information exchanges that occurred to date and a detailed 

description of our remaining concerns. NIOSH indicated that it would provide a written 

response to our concerns, but we have not yet received that material from NIOSH. 

The second part of this issue is the use of chest counts to reconstruct Th-232 internal exposures 

post-1968. Prior to the meeting, NIOSH had provided a white paper describing their approach to 

using these data to reconstruct worker doses to Th-232 and to build a coworker model using 

these data. The title of the Oak Ridge Associated Universities Team (ORAUT) white paper is 

Thorium In Vivo Coworker Study for FEMP - A Proposed Attachment for ORAUT-TKBS-0017-5, 

Rev. 1 (hereafter referred to as the ORAUT white paper) (ORAUT 2008). At the time of the 

meeting, SC&A had only begun to review the ORAUT white paper and we discussed some of 

our initial concerns. This SC&A report presents the results of its review of ORAUT 2008. The 

focus of this review is on two main topics: 

(1) The technical aspects and interpretation of available thorium in-vivo data. This issue is 

discussed in the SC&A Review Comments section, under General Comment 1. 

(2) An investigation into who was monitored for thorium and whether this subgroup of 

workers adequately covers the potential thorium exposures encountered at the Fernald 

Feed Material Production Center (FMPC). This issue is discussed in the SC&A Review 

Comments section, under General Comment 2. 

SUMMARY OF ORAUT WHITE PAPER 

The purpose of the ORAUT white paper is to explain the rationale and summarize the data 

underlying NIOSH’s proposed coworker dose model for internally deposited thorium in Fernald 

workers for whom no monitoring records or inadequate monitoring records exist. The pertinent 

exposure period is 1968–1989. An earlier document, Analysis of Coworker Bioassay Data for 

Internal Dose Assignment (ORAUT 2005), describes the general process used by NIOSH to 

analyze bioassay data for assigning doses to individuals based on coworker results. 

The underlying data are in-vivo chest count measurements of Th-232 chain members for Fernald 

workers with apparent workplace exposures to thorium. The measurements were made mainly 

during the period 1968–1989 using the Y-12 Mobile In Vivo Radiation Monitoring Laboratory 

(MIVRML). NIOSH transcribed data from 6,423 records representing more than 1,300 Fernald 

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workers, evaluated the transcribed data, modified some data, and excluded 523 samples from the 

statistical analysis, due to apparent unreliability or other reasons. 

NIOSH found that useful amounts of chest count data are available for the years 1968 through 

1988. From 1968 through 1978, the estimated thorium lung burden was reported as thorium 

mass (mg of Th-232) in nearly all cases. During 1979–1988, thorium lung burden was reported 

as activity of the Th-232 chain members Ac-228 and Pb-212 in nearly all cases. The differences 

in reporting conventions before and after 1978 were resolved by changing all reporting units to 

nCi. For the thorium data reported in mg, the mass to activity conversion assumed that all of the 

mass of natural thorium is associated with Th-232. The specific activity factor used for this 

conversion was 0.11 nCi of Th-232 per mg of natural thorium. 

NIOSH generated chest count data statistics for yearly intervals, based on specifications and 

requirements in ORAUT (2005) and ORAUT (2006). A lognormal distribution was assumed, 

and the 50th and 84th percentile values were calculated. 

NIOSH could not determine the measured quantities and assumptions underlying estimated lung 

burdens recorded as mg of thorium. Presumably, the measured quantity was gamma emissions 

from Ac-228 and/or Pb-212. NIOSH noted that measured activity of Ac-228 may not be a useful 

indicator of Th-232 activity in the lungs of Fernald workers, because chemical purification of 

thorium occurred as a routine part of thorium processing. Purification would remove Ac-228 

and, as a result, it would take many years for Th-232 and Ac-228 to re-establish secular 

equilibrium after chemical separation, due to the relatively long half-life of the intermediate 

separated chain member Ra-228. Under these circumstances, a chest count may observe little or 

no Ac-228, but substantial quantities of Th-232 may nevertheless be present. On the other hand, 

measured activity of Pb-212 is regarded by NIOSH as a useful indicator of Th-232 activity on 

the theoretical basis that the activity ratio Th-228:Th-232 would never be less than about 0.422 

following chemical separation of the Th-232 chain, and the activity ratio Pb-212:Th-228 is not 

expected to be substantially less than 1.0 in the lungs for prolonged periods. To convert in-vivo 

measurements recorded as Pb-212 to an estimated lung content of Th-232, NIOSH assumes a 

Pb-212:Th-232 ratio of 0.711 representing the midpoint between secular equilibrium (ratio of 

1.0) and the minimum theoretical ratio after chemical separation of Th-232 and Th-228 from 

other members of the Th-232 chain. 

NIOSH fit in-vivo thorium measurements (presumably referring to data for an individual worker) 

to a set of chronic inhalation scenarios involving Absorption Type M or Absorption Type S. A 

single chest count result for each period was assumed to have occurred at the midpoint of the 

period. A uniform absolute error of 1 was applied to all results, which thus assigned the same 

weight to each result. 

Assumed intakes were based on patterns observed for the time-dependent in-vivo data. Periods 

where lung count data were similar were assumed to represent periods of constant chronic intake. 

The chronic intake level was changed if the in-vivo measurements indicated a significant 

sustained change at some point, such as a nearly monotonic increase or decrease in the in-vivo 

measurements over time. 

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Geometric standard deviation (GSD) values are equal to the 84th percentile intake rates divided 

by the 50th percentile intake rates. To account for errors associated with the assigned biokinetic 

models, a GSD of 3 was assigned. 

Finally, NIOSH assumed that workers with the highest exposure potential for uranium and 

thorium would be counted most frequently. 

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1.0 SUMMARY OF FINDINGS 

SC&A performed two different kinds of analyses on the thorium in-vivo data. The first relates to 

the quality of the data. The first eight findings relate to this analysis. The remaining findings 

relate to an analysis of the quantity of data, and whether the data can be related to thorium 

workers and are adequate for dose reconstruction and a coworker model, apart from the quality 

issues raised in the first eight findings. 

The following findings relate to the quality of the thorium in-vivo data, based on the analysis in 

Section 1 of this report: 

(1) The use of in-vivo samples reported in mg of Th for the period 1968–1978 might 

significantly underestimate the lung burden of thorium, if the result was based on the 

gamma activity of thorium daughters Ac-228 and/or Pb-212. See Sections 2.1 and 2.7. 

(2) SC&A questions whether enough evidence exists to justify the conversion factor 1 mg Th 

= 0.11 nCi, based on the small number of overlapping samples in 1978–1979 that have 

been used to justify the factor. See Section 2.2. 

(3) There is a high amount of imprecision present in the pre-1979 data, as shown in 

individual worker records with implausibly large changes in reported lung burden over 

relatively short time periods. This could be explained by varying exposures to more 

heterogeneous mixtures of thorium and its daughter products, but may also have 

implications as to the reliability of in-vivo measurements during this period. See 

Section 2.3. 

(4) The reported thorium MDA of 6 mg appears incompatible with actual positive results 

reported for Fernald workers. Furthermore, the 84th percentile values presented in the 

coworker study were all below this 6 mg threshold, with the exception of 1968. See 

Section 2.4. 

(5) There is no information provided on the counting time and calibration methods for 

measuring Pb-212, which calls into question how in-vivo results are being interpreted. 

See Section 2.5. 

(6) Given the lack of information on the MDA and uncertainties on the significance of the invivo Pb-212 results, SC&A questions the credibility of the positive Pb-212 results. All 

derived results at the 84th percentile in the period 1978–1989 are positive results, yet are 

below the plausible MDAs for Pb-212. See Section 2.6. 

(7) SC&A feels more justification is required to validate the assumed Pb-212:Th-232 activity 

ratio of 0.71 (the midpoint of the theoretical range of 0.42–1). Studies suggest the ratio 

shows considerable variation and, in some cases, has been found to be significantly 

smaller than the lower bound assumed by NIOSH of 0.42. See Section 2.7. 

(8) Data for identified thorium workers suggest a large number of negative results for 

Pb-212, which may indicate an overestimation of the natural background component of 

Pb-212 and possibly a systematic underestimation of thorium lung burdens. See 

Section 2.8. 

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The following findings relate to the adequacy of data, apart from quality considerations. The 

analysis for these findings is in Section 3 of this report. 

(1) SC&A identified two resources that cover 60 individual workers, who were designated as 

thorium workers either by a 1967 memo listing thorium workers (Starkey 1967), or as 

indicated directly on their respective in-vivo monitoring logsheets. Most, but not all, of 

these workers have some in-vivo thorium monitoring data. Only limited information can 

be derived from these resources as to when these workers were involved in thorium 

operations. See Sections 3.1 and 3.4. 

(2) It has not been possible for SC&A to validate NIOSH’s assumption that the rationale for 

thorium in-vivo monitoring was preferentially oriented to workers with high thorium 

exposure potential. The pattern of monitoring does not validate that assumption. During 

the production years (1968–1979), about 88% of the in-vivo samples were not related to 

the thorium production plants and years. In other words, only about 12% of the in-vivo 

thorium measurements were in plants during years when there were known thorium 

campaigns. There is evidence that in-vivo thorium monitoring was incidental to uranium 

in-vivo monitoring, rather than being directed at workers who had high exposure 

potential for thorium. The highest thorium readings are mainly for workers who were not 

identified either as thorium workers or former thorium workers. See Section 3.2. 

(3) High in-vivo results for workers not identified as thorium workers may have arisen from 

redrumming operations; fugitive emissions in poor industrial hygiene thorium areas; 

handling of thorium from other sites by workers not identified as thorium workers, 

especially after Fernald became the national repository for thorium in 1972; or thorium 

operations that have not yet been identified, possibly due to the destruction of documents 

during declassification in the early 1970s. See Section 3.3. 

(4) SC&A has performed an extensive review of documentation for FMPC available on the 

Site Research Database (SRDB) and has not found sufficient evidence that workers 

involved in thorium operations or other workers who had significant thorium exposure 

potential (for instance due to redrumming) can adequately be identified in years 

subsequent to the start of in-vivo monitoring in 1968. See Section 3.4. 

(5) Plant documentation indicates poor industrial hygiene conditions prior to 1985, including 

in areas associated with thorium production and with thorium redrumming. Both fugitive 

emissions and redrumming operations likely created high episodic exposure potential, at 

least during some of those operations. Given the lack of data identifying these two types 

of exposures (other than for [redacted] redrumming workers), it is not possible to 

compare the intakes due to episodic exposures to those due to routine production 

exposures. In view of this, the assumption of chronic exposure using the in-vivo 

monitoring data as the mid-point of exposure may not be an appropriate basis for dose 

reconstruction, even for those with monitoring data; it would be even more problematic 

for a coworker model. See Sections 3.3 and 3.5. 

SC&A’s overall conclusions regarding the adequacy of data (i.e., setting aside issues related to 

quality of data) are that the findings taken together indicate that (1) there are significant issues 

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NOTICE:

that NIOSH has not yet addressed that raise questions about its ability to construct a coworker 

model, (2) there is no clear explanation for the fact that most of the high thorium results in the 

production period are in plants and years when there was no documented thorium production, 

and (3) there appears to be insufficient documentation so far for identifying the workers with 

exposure potential to thorium, making it unclear to whom the coworker model would be applied. 
2.0 SC&A REVIEW COMMENTS – GENERAL COMMENT 1 

NIOSH’s interpretation of in-vivo thorium measurements for Fernald workers may 

substantially underestimate the actual lung content of Th-232 + Th-228 in many cases, 

particularly for the period 1968–1978, when in-vivo measurements were reported as mg of 

thorium. 

2.1 UNCERTAINTY IN INTERPRETATION OF DATA FOR THE PERIOD 1968–

1978 

NIOSH takes the estimated thorium lung burdens for the period 1968–1978 (recorded as mg of 

thorium) at face value. Statements made in the Occupational Internal Dose TBD ORAUTTKBS-0017-5 (2004) and in the ORAUT white paper indicate, however, that the in-vivo 

measurements for this period are most likely based on gamma emissions from Ac-228, which 

may have been present in the lungs at far lower concentrations than Th-232 in many cases: 

 Page 22 of ORAUT-TKBS-0017-5: “The thorium results are questionable because of the 

lack of information for readily interpreting them (e.g., there is no information regarding 

the in-vitro separation method or counting procedure/equipment, nor is there information 

regarding the assumptions made to derive the in-vivo results). 

 Page 35 of ORAUT-TKBS-0017-5: “Thorium-232 and Th-228 activities were 

determined based on equilibrium assumptions and detection of their progeny, most likely 

Ac-228 for Th-232, but Pb-212 may have been used for assessment of both Th isotopes.” 

 ORAUT white paper: “Because of the relatively long half-life of Ra-228, the parent of 

Ac-228, and the fact that chemical purification of thorium occurred as a routine part of 

thorium processing, the measured activity of Ac-228 is unlikely to be a useful indicator 

of Th-232 activity at FMPC, especially in a generalized use such as this coworker study.” 

 As indicated in Figure 2 of the ORAUT white paper, several years are required for Ac228 to approach secular equilibrium after chemical separation of the Th-232 chain. For 

example, the activity ratio Ac-228:Th-232 in the lungs would be only about 0.06 at 

6 months after inhalation of initially pure thorium, and about 0.11 at 1 year, assuming no 

migration of in-growing Ac-228 from Th-232. 

As illustrated in Figures 1 and 2, in-vivo data for some Fernald workers recorded as mg of 

thorium show a nearly monotonic increase over a substantial portion of the observation period. 

These patterns of time-dependent measurements could arise from any number of different 

exposure scenarios, such as increasing levels of exposure to thorium over time, or chronic intake 

of highly insoluble forms of thorium at a nearly constant rate. They are also consistent with the 

assumption of a continually increasing activity of Ac-228 in the lungs resulting from its ingrowth after intake of thorium that has been chemically separated from its chain members. In 

this case, the estimated intake of Th-232 by the worker based on the in-vivo measurements 

reported as mg of thorium could greatly underestimate the actual intake of Th-232. For the 

thorium worker population as a whole, use of unadjusted in-vivo measurements reported as mg 

of thorium may be expected to result in a lesser, but perhaps still sizable, underestimate of 

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average intake, if measurements of Ac-228 were indeed used to represent the Th-232 content of 

the lungs. 

The in-vivo data for workers indicated in Figures 1 and 2 and later figures in this review are from 

a set of 60 thorium workers1

 identified by SC&A as an aid in the evaluation of NIOSH’s 

proposed method of dose reconstruction and development of a coworker model. The method of 

determination of this set of thorium workers is described later in this review. 

Figure 1: In-vivo Data for a Fernald Worker, Recorded as mg of Thorium 

The data are consistent with the assumption of inhalation of chemically separated thorium (among many exposure 

scenarios), assuming the measured quantity is the level of gamma emissions from Ac-228. 

Figure 2: In-vivo Data for a Fernald Worker, Recorded as mg of Thorium 

The data after the early 1970s are consistent with the assumption of inhalation of chemically separated thorium 

(among many exposure scenarios), assuming the measured quantity is the level of gamma emissions from Ac-228. 

 

Draft Review – Proposed Attachment 12 June 28, 2010 

1

 Note: Only 49 of the 60 workers identified as thorium workers could be found in the in-vivo database. 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.
Substantial errors in estimated intakes of Th-232 based on in-vivo data recorded as mg of 

thorium may also arise, due to disequilibrium between Th-232 and Pb-212, as indicated by 

experimental data for rats (Stradling et al., 2001). These data are discussed in a later subsection 

that addresses uncertainties associated with in-vivo data reported as activity of Pb-212 (1979–

1988). 

2.2 CONSISTENCY OF PRE-1979 AND LATER IN-VIVO THORIUM DATA 

The ORAUT white paper states that, “A minor overlap in reporting conventions occurred 

between 1978 and 1979.” That is, in each of these years, some in-vivo thorium measurements 

were reported as mg of thorium and some were reported as nCi Pb-212 and nCi Ac-228. Later in 

the white paper, a broad agreement (up to factor-of-3 differences) in either 50th percentile or 84th

percentile thorium chest burdens in each of these 2 years based on the two different reporting 

conventions is used as support for this conversion factor 1 mg of thorium = 0.11 nCi proposed in 

the ORAUT white paper. For 1978, NIOSH identified only 36 measurements on 31 workers that 

were reported as activities of Pb-212 and Ac-228. For 1979, NIOSH identified only 15 

measurements on [redacted] workers that were reported as mg of thorium. SC&A has been able 

to identify only 22 individual in-vivo samples (representing [redacted] workers) that have 

reported results for Th, Ac-228, and Pb-212 in the same count. Thus, the comparison is for small 

numbers of measurements on persons with potentially different tasks and job locations, and 

would appear to offer little support for the proposed conversion factor. 

Data for 15 individual workers with in-vivo thorium data before and after the change in reporting 

convention were examined by SC&A to determine whether the data reported in mg of thorium 

merge reasonably well with the post-1978 measurements of Ac-228 and Pb-212 after application 

of the conversion factor 1 mg Th = 0.11 nCi. The data for some subjects were found to merge 

reasonably well around the transition period, as illustrated in Figure 3, while data for others were 

inconclusive. A discontinuity between the 1968–1978 and 1979–1988 datasets was evident in 

one case (Figure 4). 

Figure 3: Example of In-vivo Data for a Fernald Worker showing a Reasonably 

Continuous Transition of pre-1979 In-vivo Measurements with Later Measurements, using 

the Conversion Factor 1 mg Th = 0.11 nCi for pre-1979 Data Proposed by NIOSH 

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Figure 4: In-vivo Data for a Fernald Worker for whom pre-1979 Data Clearly 

Do Not Merge with Later Data 

Furthermore, SC&A identified 22 entries that reported both Th (mg) and Pb-212 (nCi), which 

allows for the direct comparison shown in Table 1. The equivalent thorium activity was 

calculated from both the thorium mass (by multiplying by 0.11 nCi/mg) and the Pb-212 activity 

(by dividing by the assumed equilibrium factor of 0.71). The last column in the table presents 

the ratio of these calculated activities. As seen in this column, the ratio of calculated activities 

fluctuates significantly, with no observable pattern. 

 

Table 1: Comparison of Calculated Thorium Activities Based on Thorium Mass (mg) 

and Pb-212 Activity (nCi) 

Reported 

Thorium 

Result (mg) 

Equivalent Activity 

Calculated by Thorium 

Mass (nCi)* 

Reported Pb-212 

Activity (nCi) 

Equivalent Activity 

Calculated from Pb-212 

Activity (nCi)** 

Ratio of Thorium 

Activities 

-5.00 -0.55 -0.04 -0.06 0.10 

-0.60 -0.07 -0.08 -0.11 1.71 

-0.54 -0.06 -0.18 -0.25 4.27 

-0.16 -0.02 -0.16 -0.23 12.80 

-0.12 -0.01 0.06 0.08 -6.40 

-0.05 -0.01 -0.05 -0.07 12.80 

-0.01 0.00 -0.01 -0.01 12.80 

0.01 0.00 -0.06 -0.08 -76.82 

0.30 0.03 0.15 0.21 6.40 

1.81 0.20 -0.10 -0.14 -0.71 

2.10 0.23 0.19 0.27 1.16 

2.10 0.23 0.25 0.35 1.52 

2.10 0.23 0.27 0.38 1.65 

2.10 0.23 0.28 0.39 1.71 

2.10 0.23 0.29 0.41 1.77 

2.10 0.23 0.30 0.42 1.83 

2.10 0.23 0.40 0.56 2.44 

Draft Review – Proposed Attachment 14 June 28, 2010 

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Draft Review – Proposed Attachment 15 June 28, 2010 

Table 1: Comparison of Calculated Thorium Activities Based on Thorium Mass (mg) 

and Pb-212 Activity (nCi) 

Reported 

Thorium 

Result (mg) 

Equivalent Activity 

Calculated by Thorium 

Mass (nCi)* 

Reported Pb-212 

Activity (nCi) 

Equivalent Activity 

Calculated from Pb-212 

Activity (nCi)** 

Ratio of Thorium 

Activities 

2.10 0.23 0.40 0.56 2.44 

2.10 0.23 0.40 0.56 2.44 

2.20 0.24 -0.10 -0.14 -0.58 

4.30 0.47 -0.04 -0.06 -0.12 

5.10 0.56 -0.04 -0.06 -0.10 

 *Calculated by multiplying thorium mass by assumed specific activity of 0.11 nCi per mg of thorium 

**Calculated by dividing Pb-212 activity by the assumed equilibrium ratio of 0.71 

2.3 APPARENTLY HIGH IMPRECISION IN PRE-1979 IN-VIVO THORIUM 

MEASUREMENTS 

For some Fernald workers, the in-vivo measurements recorded as mg of thorium show 

implausibly large changes for inhaled thorium over brief time periods. For example, [redacted] 

had an estimated chest burden of 10.2 mg Th on [redacted], but only 0.2 mg Th about 40 days 

later. As illustrated in Figures 3 and 5, the data recorded as mg of thorium generally are more 

variable over time than the later data recorded as activities of Ac-228 and Pb-212. This could be 

related to improvements in the measurement techniques over time, but could also be the result of 

changes in the nature of the work or the forms of thorium handled. Thorium processing at 

Mound was completed in 1979, with exposure from that time being limited to repackaging and 

shipping operations (ORAUT-TKBS-0017-5). It may be that the equilibrium assumptions used 

to interpret in-vivo data are more nearly correct for thorium workers overall for the period 1979–

1988 than for the period 1968–1978, when workers could have encountered more heterogeneous 

materials and more widely varying activity ratios of members of the Th-232 chain. 

Figure 5: Data for a Thorium Worker Illustrating the Typically Higher Variability of 

In-vivo Thorium Measurements Recorded as mg of Thorium than of Later Measurements 

Recorded as Activities of Ac-228 and Pb-212 

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2.4 INCOMPATIBILITY OF FERNALD IN-VIVO THORIUM DATA RECORDED 

AS MG OF THORIUM WITH THE MDA FOR TH-232 GIVEN IN ORAUTTKBS-0017-5 

The Internal Dosimetry TBD ORAUT-TKBA-0017-5 gives an MDA of 6 mg for Th-232 for the 

external counting method used at Fernald. It is not explained how this MDA was derived, nor 

which nuclide was used to derive the MDA or the counting time, if there was a standard counting 

time. On page 6 of ORAUT 2008, a table of in-vivo counting statistics is given. Table 1 of 

ORAUT 2008 shows that the 84th percentiles for all years except 1968 are below the 6 mg MDA. 

The results that exist for thorium are not compatible with the 6 mg MDA. 

2.5 LACK OF INFORMATION ON THE MIVRCL SYSTEM AND CALIBRATION 

FOR PB-212 

The Occupational Internal Dosimetry TBD, ORAUT-TKBS-0017-5, gives the following 

information, on page 36, item 5.3.8: 

The In Vivo Examination Center (IVEC) operated at the FCP from 1989 to 2001, 

a subject with a [redacted] chest wall thickness had the MDAs listed in Table 5-

26 at the 95% confidence interval for a 3,600 sec count. The previous mobile 

counting system, which serviced Fernald from 1968 to 1989, provided reports to 

the site. However, no system performance characteristics have been discovered 

to date. 

There is no information on the counting time for the earlier system. There is also no information 

on the calibration of Pb-212 for lung counting, including influence from cross irradiation from 

bone. 

2.6 LACK OF INFORMATION ON THE MDA AND UNCERTAINTIES ON THE 

SIGNIFICANCE OF THE IN-VIVO PB-212 RESULTS 

The Occupational Internal Dosimetry TBD, ORAUT-TKBS-0017-5, page 36, Table 5-26, 

assigns an MDA equal to 6 mg for Th-232 for the period 1968–1989, assumed to correspond to 

0.66 nCi. Using the 0.711 equilibrium factor suggested in NIOSH’s white paper, this MDA 

corresponds to about 0.5 nCi of Pb-212. Table 2 of the white paper (page 7) gives the in-vivo 

lung counting statistics for 1978–1989. All 84th percentiles are below the MDA, and in many 

years, the values are one order of magnitude below the MDA. The MDA for Pb-212 (about 

0.5 nCi) is an acceptable value, although there is a lack of information on the counting time. 

NRPB Publication 57, 2004, cites 20 Bq (0.54 nCi) as an acceptable MDA for Pb-212. 

Some laboratories present an MDA of about 8–9 Bq (about 0.21–0.25 nCi), for an 8” × 4” 

detector, 60-min counting time, in a shielded room whole-body counter installation. Other 

laboratories report the same limit for germanium detectors, 30-min counting time, in a shielded 

whole-body counter installation. 

Draft Review – Proposed Attachment 16 June 28, 2010 

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Draft Review – Proposed Attachment 17 June 28, 2010 

In the O-Drive, a 1979 Union Carbide document about Mobile Counter sensitivities (Union 

Carbide 1979) states that the sensitivities of the Mobile Counter, calculated for the 95% 

confidence level, taken to be 1.96 sigma, were derived by calculating the standard deviations 

from source and control subject runs. The two were mathematically combined using the 

relationship σt = (√σs

2

 + σc

2 ), where σt is the total standard deviation, σs is the source run

standard deviation, and σc is the control run standard deviation. The sensitivity for Pb-212 is 

listed as 0.23 nCi.2

 The counting time is listed as 2,000 sec. 

All 84th percentiles reported in Table 2 of NIOSH’s white paper are below the MDA of 0.21 nCi, 

and in many years, the values are 1 order of magnitude below the MDA. 

SC&A questions the significance and creditability of the positive Pb-212 results, since all 84th

percentiles in the period 1978–1989 are positive results and are below plausible MDAs. 

2.7 EQUILIBRIUM, ACTIVITY RATIOS, AND INTERPRETATION OF PB-212 

RESULTS, 1978–1988 

NIOSH applies the activity ratio Pb-212: Th-232 = 0.711 as the midpoint of the theoretical range 

0.422–1.0. The lower bound 0.422 is the theoretical minimum activity ratio Th-228: Th-232 

following chemical separation of Th-232 and Th-228 from the other chain members. It is 

assumed that Th-232 chain members produced in the lungs after inhalation of Th-232 will have 

the same kinetics as Th-232 in the lungs. 

Autopsy data for thorium workers in general are not entirely consistent with this hypothetical 

lower bound ratio Th-228:Th-232. For example, in lung tissues from [redacted] thorium 

workers, the ratio Th-228:Th-232 was in the range 0.24–0.47 and averaged 0.35 (Stehney and 

Lucas 2000). On the other hand, the average ratio Th-228:Th-232 was 0.93 in the insoluble 

residue in the lungs of [redacted] persons exposed to monazite ore and thorium (Lucas and 

Stehney 1988). 

Stradling et al. (2001) measured the activity ratio Th-232:Pb-212 in lungs of rats exposed to 

Th-232 + Th-228 by intratracheal administration. The ratio Th-232:Pb-212 was determined as a 

function of time following administration of different chemical forms and masses of thorium. 

Results are summarized in Figures 6 and 7. For most of the tested forms and masses of thorium, 

the ratio is substantially greater than predicted from theoretical disequilibrium fractions and the 

assumption that all chain members have the same kinetics in the lungs. Large activity ratios 

Th-232:Pb-212 even occurred in some cases for highly insoluble particles containing thorium as 

dioxide. The investigators conjectured that migration of the short-lived progeny occurred as 

some combination of diffusion of Rn-220 and recoil of the progeny due to alpha particle decay, 

as both mechanisms have been observed in vitro. These results seem pertinent to evaluation of 

thorium exposure at Fernald, where the main chemical forms of thorium associated with thorium 

plant processes were listed by NIOSH (ORAUT 2004) as thorium metal, ThO2, Th(OH)4, and 

ThNO3. 

 2

 The lead isotope mass number is not given in the document. We assume it is lead-212. 

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Figure 6. Activity Ratio Th-232:Pb-212 in Lungs of Rats as a Function of Time 

after Intratracheal Instillation of Different Masses of Th-232 + Th-228 

as Thorium Dioxide or Hydroxide 

(Data from Stradling et al. 2001) 

Figure 7. Activity Ratio Th-232:Pb-212 in Lungs of Rats as a Function of Time after 

Intratracheal Instillation of Different Masses of Th-232 + Th-228 

as Thorium Nitrate or Fluoride 

(Data from Stradling et al. 2001) 

Draft Review – Proposed Attachment 18 June 28, 2010 

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Draft Review – Proposed Attachment 19 June 28, 2010 

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2.8 POSSIBLE OVERESTIMATES OF BACKGROUND FOR PB-212 

For several individuals in a group of 60 workers identified by SC&A as thorium workers at the 

start of the in-vivo thorium monitoring program, all or nearly all measurements specifically 

identified as Pb-212 measurements are negative, as illustrated in Figures 8 and 9. This suggests 

an overestimate of natural background for Pb-212 and hence a potential systematic underestimate 

of lung burden of Th-232, based on in-vivo measurements of Pb-212. 

Figure 8. Example of a Thorium Worker for Whom Nearly All In-vivo Pb-212 

Measurements are Negative 

Figure 9. Example of a Thorium Worker for Whom Nearly All In-vivo Pb-212 

Measurements are Negative 

NOTICE:
3.0 SC&A REVIEW COMMENTS – GENERAL COMMENT 2 

NIOSH has not demonstrated that the in-vivo thorium monitoring was preferentially 

oriented to workers with high exposure potential. Data indicate that thorium monitoring 

may have been incidental to uranium in-vivo monitoring. Most of the above MDA results 

during the production period are not for identified thorium workers or former thorium 

workers, nor are they for thorium production plants and years. Furthermore, there exists 

the potential for episodic thorium exposure to workers involved in redrumming operations, 

which occurred periodically for decades, or episodic exposure due to fugitive emissions. 

NIOSH has not demonstrated that a chronic exposure model would be valid for episodic 

exposures. Significant issues remain that raise questions about NIOSH’s ability to 

construct a coworker model and whether the available data are adequate for that purpose. 

In this section, we will take thorium lung burden data at face value (i.e., we set aside the quality 

issues discussed in Section 1) and examine the characteristics of measurements of workers 

identified as thorium workers and others who were not so identified in any document that SC&A 

found, but who were monitored for thorium. This allows at least a partial examination of the 

adequacy of data for thorium dose reconstruction and for creating a coworker model. 

3.1 IDENTIFICATION OF THORIUM PRODUCTION WORKERS AND 

ASSOCIATED DATA 

SC&A identified only two sources for identifying thorium production workers. 

 A list of thorium workers compiled by Bob Starkey, dated December 26, 1967 (referred 

to as the ‘Starkey memo’ in this report), lists 51 individuals (Starkey 1968). 

 A compilation of in-vivo logsheets that have ‘Th worker’ ([redacted] individuals) or 

‘former Th worker’ (17 individuals) written on them. (The document has no cover sheet 

and no author. It contains Privacy Act-protected data, and is located on the O-Drive.) 

There was some overlap between the two resources, so there are 60 total individuals identified 

between the 2 documents. These two resources are discussed in the following two subsections. 

Here we note that the number of these individuals who were employed during the 1968–1989 

period declined steadily during the 1968–1979 production period. The proportion of those still 

working who were monitored was generally in the 60% to 80% range, with the notable 

exceptions of 1969 and 1970. Figure 10 shows the number of the 60 thorium workers employed 

in each year of the MIVRML operation, as well as the percentage of those employed that also 

had a non-blank entry for either ‘Th,’ ‘Pb212,’ or ‘Ac228’ in that year. 

Draft Review – Proposed Attachment 20 June 28, 2010 

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0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

1968

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

Year

% of Monitored Th Workers

0

10

20

30

40

50

60

# of Th Workers in Year

% '60 Th Workers' Monitored

# '60 Th Workers' in Year

Figure 10. For the ‘60 Th workers’ Identified by SC&A, the Number Employed by Year 

and the Percentage Monitored by Year 

3.1.1 Starkey Memo 

The Starkey memo was written late in December of 1967 and identifies 51 individuals who are 

designated as thorium workers. It is plausible that these workers were identified as thorium 

workers for the coming year; however, it is also possible they were simply the thorium workers 

for the previous year (1967). Of these 51 workers, approximately 55% were monitored for 

thorium in 1968. Given that 168 workers were monitored for thorium in 1968, and that just over 

half of the 51 workers identified as thorium workers for that time were monitored in that year, it 

appears that the ORAUT white paper statement that, “Workers identified to have potential 

exposures to thorium were given priority for counting during the first use of the MIVRML” is 

not fully borne out by the data (ORAUT 2008, p. 4). We assume that the phrase, “the first use of 

the MIVRML,” refers to the first year of its use for thorium data, which was 1968. Overall, 78% 

of those identified in the Starkey memorandum were monitored for thorium at some point during 

their employment, and the rest have no monitoring for thorium during their career. 

Draft Review – Proposed Attachment 21 June 28, 2010 

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SC&A examined the 1968 in-vivo monitoring for these 51 thorium workers and compared it to 

all those monitored in 1968. The results are shown rank ordered in Figure 11.3 Based on 

Figure 11, those workers designated as thorium workers in the Starkey memo have higher invivo thorium results in 1968 than the monitored worker population as a whole in 1968. 

However, the interpretation of this fact is complicated by the fact that almost 75% of the samples 

associated with these thorium workers indicate the employee was working in either Plant 5 or 

Plant 9, though no known thorium operations were undertaken in either plant at this time (Morris 

2008). Please refer to Table 2 in Section 3.2 of this report for a list of years and plants where 

thorium is known to have been produced. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-3 -2 -1 0 1 2 3 4 5 6 7 8 9

Th Lung Burder (mg)

Rank Ordered Percentile

51 Thorium Workers from Starkey Memo

All Monitored Workers

Figure 11. Rank Ordered 1968 Thorium Lung Burden (in mg Th) for 51 Thorium 

Workers Identified in Starkey Memo Compared to All Monitored Workers in 1968 

 

Draft Review – Proposed Attachment 22 June 28, 2010 

3

 Excel database “Composite In Vivo with E Brackett 01-08-07 final approved database,” in the O Drive/ 

AB Document Review/Fernald/FMPC MIVRML 1968–1987, which summarizes the in-vivo count data, hand 

written results contained in the files FEMP 1, FEMP 2, FEMP 3, FEMP 3a, FEMP 4, FEMP 5, FEMP 6, FEM 7, 

FEMP 8, FEMP 9, FEMP 10, FEMP 11, FEMP12, FEMP 13, FEMP 14, FEMP 15, FEMP 16, FEMP 17, FEMP 18, 

FEMP 19, FEMP 20, and FEMP 21. SC&A has not verified if all data were copied into the Excel database, nor the 

degree of accuracy in the transcription. However, through the course of this investigation, there have been instances 

noted where an Ac-228 and a Pb-212 result in the hardcopy were incorrectly transcribed as a Th and Ac-228 in the 

database. Other less important discrepancies were identified, such as incorrect badge numbers or reference page 

numbers in the hardcopy. 

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Health for factual accuracy or applicability within the requirements of 42 CFR 82.
3.1.2 Thorium Workers Identified by Individual In-vivo Logsheets 

As stated previously, 26 workers had the label ‘thorium worker’ or ‘former thorium worker’ 

written at the top of their individual in-vivo logbook records. It is currently not known what the 

difference between a ‘thorium worker’ and a ‘former thorium worker’ is, nor is it clear how this 

label applies to the individual samples and employment periods. The 26 individual workers 

represent 305 samples during the thorium production period (1968–1979). However, only 21% 

of these 305 samples were associated with plants where production was known to occur. 

Furthermore, 12 of the 26 workers (approximately 46%) do not appear to have any samples taken 

at known thorium production plants. 

The in-vivo logsheets also contain data on the plants associated with the in-vivo samples and, of 

course, the dates of the sampling. It is therefore possible to compare the in-vivo results for the 

26 workers identified in the logsheets as thorium and former thorium workers with those for 

workers not so identified. The 305 records for the 26 workers are broken into two parts; those 

associated with thorium facilities, and those that indicate a plant or area of the site not known to 

be directly involved in thorium production. Figure 12 shows almost all the data points for the 26 

workers and all workers monitored for thorium. The scale for thorium is cut off at 8 mg in 

Figure 12, but 24 data points are above this figure.4

 Figure 13 includes all data points, including 

the very highest thorium measurements above 8 mg. 

As is clear from Figure 12, the thorium worker records associated with thorium production 

facilities are generally higher than non-production facilities, except at the higher end of the 

measurement results. At the upper end of the Figure 12, the higher values of thorium lung 

burdens are those for “thorium workers” or “former thorium workers” in non-thorium facilities. 

Furthermore, the very highest results, from 6 mg to 32.5 mg of thorium, shown in Figure 13, are 

mainly for workers who are not identified as thorium workers or former thorium workers. 

Specifically, the NIOSH in-vivo thorium database shows that there were 76 in-vivo thorium 

measurements in the production period at or above the MDA of 6 mg. Of these 76 

measurements, only 20 (just over 1⁄4) are identified in the in-vivo records as measurements for 

thorium or former thorium workers. Furthermore, only 9 of the 76 measurements, or about 12%, 

are identified with thorium production plants and years. 

The tendency for higher results in non-thorium plants and non-thorium production periods may 

be due to one or more factors, such as exposures resulting from redrumming operations, fugitive 

emissions, thorium production operations that have not yet been identified, or some other factor 

or some combination of factors (see Section 3.3). 

Draft Review – Proposed Attachment 23 June 28, 2010 

 4

 One high result of 303 mg has been omitted as an erroneous outlier in this analysis. Also the lowest 

negative result of -117.8 mg was not included. SC&A has not analyzed this issue here, because it does not affect the 

analysis in this section. 

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Health for factual accuracy or applicability within the requirements of 42 CFR 82.
Comparison of Rank Ordered Th Results for Workers with "Thorium" and 

"Former Thorium" Written on Their In Vivo Logbook Versus All Workers

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-2 -1 0 1 2 3 4 5 6 7 8

Mg Thorium

Rank Order

Thorium Worker Records at Th Facilities

Thorium Worker Records at Non-Th

Facilities

All Worker Th In Vivo

Figure 12. Rank Ordered In-vivo Results (mg of Th) for All Monitored Workers and 

Thorium Workers (at both Thorium Production Facilities and Non-production Facilities) 

for the Thorium Production Period (1968–1979) 

Comparison of Rank Ordered Th Results for Workers with "Thorium" and 

"Former Thorium" Written on Their In Vivo Logbook Versus All Workers

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

Mg Thorium

Rank Order

Thorium Worker Records at Th Facilities

Thorium Worker Records at Non-Th

Facilities

All Worker Th In Vivo

Figure 13. Rank Ordered In-vivo Results (mg of Th) for All Monitored Workers and 

Thorium Workers (at both Thorium Production Facilities and Non-production Facilities) 

for the Thorium Production Period (1968–1979) 

Draft Review – Proposed Attachment 24 June 28, 2010 

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Data on the 26 “thorium workers” and “former thorium workers” (as identified by their 

logsheets) for the known production period are displayed by year in Figure 14. It is clear that for 

most years, the highest in-vivo results are for former thorium workers, as compared to thorium 

workers. Furthermore, there is no information on the period of time the former thorium workers 

were exposed to thorium. Also, SC&A has discovered no specific criteria on what was meant by 

the classification ‘thorium worker’ or on the period of time that workers in this classification 

were exposed. There is also no definition of the term “former thorium worker.” This creates a 

problem on how these data should be interpreted for a coworker model. 

Th in mg in vivo

-12

-9

-6

-3

0

3

6

9

12

15

1966 1968 1970 1972 1974 1976 1978 1980

year

result 

former th workers

Th workers

Figure 14. In-vivo Results in mg of Thorium for 9 “Thorium Workers” and 17 “Former 

Thorium Workers” as Identified by Their Individual Logbooks 

Figure 15 compares the data in mg of thorium by year for the “thorium workers” and “former 

thorium workers” with all in-vivo data for all workers monitored for thorium. It shows that in 

most years, the very highest results were for workers who were neither identified as “thorium 

workers” nor “former thorium workers.” Moreover, most of these were associated with nonthorium production plants and times (see discussion in this section above; Section 3.2, Table 2; 

and Sections 3.3 and 3.5). 

Draft Review – Proposed Attachment 25 June 28, 2010 

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Th in mg in vivo

-20

-10

0

10

20

30

40

1967 1969 1971 1973 1975 1977 1979

year

result 

all

former th workers

Th workers

Figure 15. Comparison of In-vivo Data in mg of Thorium from the Identified “Thorium 

Workers” and “Former Thorium Workers” with All In-vivo Results Found in NIOSH’s 

Excel Database 

3.2 IN-VIVO MONITORING BY PLANT DURING THORIUM PRODUCTION 

PERIODS 

Independently of the specific identification of thorium workers, SC&A examined whether there 

was in-vivo monitoring coverage for plant areas that were known to process thorium compounds 

by year. Information regarding which plants were involved in thorium production by year is 

provided in Morris 2008. Table 2 lists the number of thorium in-vivo samples associated with 

each plant and year, and also indicates the percentage of the total in-vivo samples taken in that 

year. Entries in Table 2 shown in bold and italicized represent plants and years where known 

thorium campaigns occurred. The data from Table 2 are also shown visually in Figure 16. It is 

important to note that the presence of sampling data for a particular plant and year that processed 

thorium does not necessarily mean the sampling was performed on the workers directly involved 

in thorium production. 

As shown in Table 2, the majority of known thorium production operations during the in-vivo 

monitoring period occurred in Plant 1 and the Pilot Plant, with scattered campaigns in other 

plants in 1968–1971. There are two instances where thorium production has been identified in a 

plant/year in which no thorium in-vivo data have been identified; Plant 1 (1969) and Plant 3 

(1968). On average, only about 12% of the in-vivo monitoring data points are associated with 

thorium production plants and times, though the timing of the sampling in relation to the thorium 

campaigns within these plants has not been established. Similar to the findings of the Starkey 

memo (and shown in Table 2 and Figure 16), a large fraction of in-vivo sampling was performed 

Draft Review – Proposed Attachment 26 June 28, 2010 

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for Plant 5, where there is no current evidence that thorium operations occurred. This indicates 

that thorium monitoring may not have been focused specifically on thorium operations or on 

workers who were involved in thorium operations in the years when they were taking place. 

SC&A explored whether the thorium monitoring may have been incidental to uranium 

monitoring, rather than targeted specifically at workers who were involved in processing and 

handling thorium in the plants and the periods when they did such thorium-related work. This 

appears to have been the case. This is indicated by the fact that 95% of all in-vivo monitoring 

contained both a uranium and thorium result, and 5% contained only uranium results. Moreover, 

there were no instances of in-vivo results containing only thorium data. 

The coworker model proposed by NIOSH does not distinguish between workers in the thorium 

plants and those who were not associated with thorium production in a particular year (ORAUT 

2008). This appears to be linked to the following assumption: 

The memo explains that those workers with the highest uranium and thorium 

exposure potential would be counted most frequently and those with virtually no 

exposure potential would not be routinely counted at all. [ORAUT 2008, p. 4] 

All plants at Fernald processed uranium, which was the main material processed. Typically, it 

was processed throughout the year. In-vivo monitoring for uranium may have been done on 

workers with the highest uranium exposure potential or in plants with higher dust 

measurements.5

 The mere fact that thorium data were collected along with uranium data does 

not indicate that workers with the highest thorium exposure potential were monitored. This may 

not have been the case, since the in-vivo thorium monitoring appears to have been incidental to 

uranium monitoring. About 88% of the in-vivo counts were taken at times and in areas where 

there was no thorium production (see Table 2). Furthermore, there appears to be no systematic 

identification of thorium workers, and not all workers who were identified as thorium workers 

were monitored. Finally, the very highest results for thorium lung burden in the 1968–1979 

production period are for workers who were not identified as thorium workers or former thorium 

workers in the documents discussed above. This includes almost three-fourths of the results 

above the MDA. NIOSH has not established that the workers with the highest exposure potential 

to thorium were monitored. Based on the available information so far, it may not be possible to 

establish who they were and whether they were monitored. Indeed, as discussed above and 

below, the whole question of identification of workers who had significant thorium exposure 

potential is a complex and, as yet, unresolved issue. 

Table 3 shows the magnitude of in-vivo counting results at the 50th percentile for the plants 

involved in thorium production as a ratio of the 50th percentile for all monitored workers. 

Table 4 presents similar information at the 84th percentile. These two tables show that in the vast 

majority of cases for Plant 1, Plant 2/3, and Plant 8, the ratios are close to 1 (within 10% of 1) or 

less than 1. In these cases, the fact that a monitored worker was in one of these plants where 

Draft Review – Proposed Attachment 27 June 28, 2010 

 5

 SC&A has not investigated whether the workers with in-vivo monitoring for uranium had the highest 

exposure potential for uranium. This is not relevant to the present report. Moreover, NIOSH is proposing to use 

urinalysis data for its uranium coworker model; hence, the issue of uranium in-vivo monitoring potential is not 

germane in the SEC context. 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.
Draft Review – Proposed Attachment 28 June 28, 2010 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

NOTICE:

thorium was processed has essentially no value in creating a claimant-favorable coworker model, 

much less in establishing a bounding intake value. In fact, in these cases, the results indicate that 

the thorium exposures in the plants not involved in thorium production were generally higher 

than those that were. In the case of the single year of production in Plant 6, the results are higher 

for thorium workers (both median and 84th percentile). The Pilot Plant monitoring data indicate 

higher 50th percentile values in most, but not all, years than all monitored workers. As noted 

above, almost three-fourths the values at or above the MDA of 6 mg were for workers who are 

not designated as thorium workers or former thorium workers in any document that SC&A has 

found. It is also important to note that the number of data points in the thorium production plants 

is quite small (less than 10) in several years. Taken together, it is not apparent how these data 

can be used to create a bounding intake, or even consistently claimant-favorable intake estimates. 

In this context, it is important to note again that the source of the higher thorium lung burdens at 

the upper end of the distribution for workers in non-thorium production plants and years has not 

been established. It could be due to episodic operations, such as redrumming, episodic exposure 

to fugitive emissions, production operations for which records have not been discovered 

[possibly due to the destruction of “a large number of records and files...in the early 1970s 

during declassification efforts” (ORAUT 2004, p. 18)], or handling of incoming thorium 

shipments from the time Fernald became the national storage site for thorium-232 in 1972 

(ORAUT 2004, p. 19) by workers not identified as thorium workers. In view of these 

uncertainties, the assignment of intake values to workers would also pose significant problems. 
Table 2. Number of Th In-vivo Samples by Plant and Year, and the Percentage of Total Thorium In-v

Number of In-vivo Results (Th) by Plant and Year, [Number (%)] Year 

Pilot Plant Plant 1 Plant 2 Plant 2-3 Plant 3 Plant 4 Plant 5 Plant 6 Plant 7 Plant 8 Plant 9 “

1968 17 (5.4%) 8 (2.6%) 1 (0.3%) 4 (1.3%) 0 (0.0%) 5 (1.6%) 76 (24.3%) 19 (6.1%) 16 (5.1%) 39 (12.5%) 35 (11.2%) 1969 3 (3.3%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 2 (2.2%) 50 (54.3%) 0 (0.0%) 3 (3.3%) 4 (4.3%) 10 (10.9%) 1970 13 (7.4%) 8 (4.5%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 22 (12.5%) 43 (24.4%) 13 (7.4%) 13 (7.4%) 16 (9.1%) 11 (6.3%) 1971 27 (4.2%) 19 (3.0%) 24 (3.8%) 32 (5.0%) 2 (0.3%) 23 (3.6%) 68 (10.7%) 78 (12.2%) 27 (4.2%) 27 (4.2%) 22 (3.4%) 

(

1972 21 (7.6%) 10 (3.6%) 19 (6.9%) 26 (9.5%) 1 (0.4%) 18 (6.5%) 38 (13.8%) 22 (8.0%) 21 (7.6%) 0 (0.0%) 11 (4.0%) 

(

1973 12 (5.5%) 11 (5.0%) 3 (1.4%) 34 (15.5%) 0 (0.0%) 7 (3.2%) 41 (18.6%) 16 (7.3%) 12 (5.5%) 0 (0.0%) 12 (5.5%) 

(

1974 14 (4.7%) 12 (4.1%) 0 (0.0%) 38 (12.8%) 0 (0.0%) 23 (7.8%) 36 (12.2%) 17 (5.7%) 14 (4.7%) 0 (0.0%) 20 (6.8%) 

(

1975 3 (1.3%) 9 (3.8%) 0 (0.0%) 56 (23.7%) 0 (0.0%) 15 (6.4%) 27 (11.4%) 11 (4.7%) 3 (1.3%) 0 (0.0%) 10 (4.2%) 

(

1976 4 (1.8%) 9 (4.1%) 0 (0.0%) 47 (21.4%) 0 (0.0%) 7 (3.2%) 35 (15.9%) 9 (4.1%) 3 (1.4%) 12 (5.5%) 7 (3.2%) 

(

1977 22 (10.0%) 6 (2.7%) 0 (0.0%) 23 (10.5%) 0 (0.0%) 6 (2.7%) 35 (16.0%) 11 (5.0%) 22 (10.0%) 6 (2.7%) 9 (4.1%) 

(

1978 21 (9.9%) 5 (2.3%) 0 (0.0%) 6 (2.8%) 0 (0.0%) 6 (2.8%) 42 (19.7%) 15 (7.0%) 21 (9.9%) 6 (2.8%) 6 (2.8%) 

(

1979 17 (8.3%) 4 (2.0%) 0 (0.0%) 7 (3.4%) 0 (0.0%) 20 (9.8%) 39 (19.0%) 7 (3.4%) 17 (8.3%) 1 (0.5%) 12 (5.9%) 

(

Total 174 (5.6%) 101 (3.3%) 47 (1.5%) 273 (8.8%) 3 (0.1%) 154 (5.0%) 530 (17.1%) 218 (7.0%) 172 (5.5%) 111 (3.6%) 165 (5.3%) 

(

Note: Bold and italicized entries represent plants and years in which known thorium campaigns were undertakencompiled by NIOSH as part of the thorium in-vivo data compilation. Timeline is from Morris 2008. Draft Review – Proposed Attachment 29 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Work

Health for factual accuracy or applicability within the requirements of 42 CFR 82.
0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

45.0%

50.0%

1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980

Year

Percentage of Total Th In Vivo Samples

Pilot Plant Plant 1

Plant 5 Mech

Other Plants (2-4, 6-9) Other Site Locations

Figure 16. Percentage of the Total In-vivo Thorium Samples by Plant for the Year 

Table 3. Ratio of In-vivo Results (mg Th) for Thorium Production Plants versus All 

Monitored Workers at the 50th Percentile 

Ratio: Production Plant/All Workers 

Year 

All Monitored 

Workers 

(mg/Th) Pilot Plant Plant 1 Plant 2/3 Plant 3 Plant 6 Plant 8 

1968 1.80 1.75 1.00 0.28 NR – 1.00 

1969 2.60 1.08 1.01 – – – 0.42 

1970 2.10 1.38 0.10 – – 1.90 0.86 

1971 2.30 1.24 0.85 – – – 0.91 

1972 2.00 0.78 1.25 – – – – 

1973 1.60 1.63 1.28 – – – – 

1974 1.05 0.95 1.05 – – – – 

1975 1.00 0.00 0.70 – – – – 

1976 1.20 2.58 0.17 – – – – 

1977 1.00 1.70 0.30 – – – – 

1978 1.90 1.50 1.16 – – – – 

1979 2.10 0.52 1.00 – – – – 

Average Ratio: 1.26 0.82 0.28 – 1.90 0.80 *NR indicates that no records were available for comparison 

Draft Review – Proposed Attachment 30 June 28, 2010 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.
Table 4. Ratio of In-vivo Results (mg Th) for Thorium Production Plants versus All 

Monitored Workers at the 84th Percentile 

Ratio: Production Plant/All Workers 

Year 

All Monitored 

Workers 

(mg/Th) Pilot Plant Plant 1 Plant 2/3 Plant 3 Plant 6 Plant 8 

1968 3.80 1.57 0.76 0.74 NR – 0.89 

1969 5.79 0.68 NR – – – 0.79 

1970 4.22 0.95 0.49 – – 1.25 0.73 

1971 4.10 1.16 0.97 – – – 0.73 

1972 3.70 0.73 0.83 – – – – 

1973 3.10 1.21 0.92 – – – – 

1974 3.14 1.00 1.50 – – – – 

1975 3.20 0.71 0.84 – – – – 

1976 3.50 2.39 0.75 – – – – 

1977 2.60 1.08 0.72 – – – – 

1978 4.10 1.04 0.93 – – – – 

1979 2.10 1.00 NR – – – – 

Average Ratio: 1.13 0.87 0.74 – 1.25 0.79 *NR indicates that no records were available for comparison 

3.3 EPISODIC EXPOSURE POTENTIAL INVOLVING THE REDRUMMING OF 

THORIUM MATERIALS 

The disposition of stored thorium compounds at Fernald was a significant concern at various 

times during site operations, as it was found that the containers storing the thorium materials 

often degraded quickly, due to environmental factors and the corrosive nature of the material. 

Therefore, repackaging and redrumming the stored thorium material was a necessary activity at 

the site and created the potential for exposure to thorium. A 1965 memo notes the continuing 

problem of drum condition, as well as the problems associated with repackaging: 

The thorium residue drums are disintegrating. [Redacted] started redrumming 

these residues but was stopped by the IH&R Department due to high levels of 

contamination arising from dust generated by the redrumming operation... About 

30% of the drums are so corroded that they cannot be lifted off their pallets 

without falling apart. This is the fourth time that this material has been 

redrummed. [DeFazio 1965] 

A 1968 memo regarding problems with thorium processing, in particular drumming operations, 

states: 

As you well know, most of our air dust problems at the FMPC over the years have 

resulted from drumming and dumping dry materials. Any time that we can 

eliminate either of these operations our air dust problems become greatly 

lessened. [Starkey 1968] 

Draft Review – Proposed Attachment 31 June 28, 2010 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.
Minutes from a 1972 meeting, as well as a memo from 1979 regarding the transfer of thorium 

drums, document the ongoing problem of degradation of thorium drums: 

A substantial number of drums containing thorium residues on inventory north of 

Plant 9 are deteriorating (primarily the T007 and T067 material) to the point that 

many require immediate redrumming. [Neblett 1972] 

We recommend that the thorium residues be disposed of as set forth in Item 1.6 

We feel environmentally that this is the better method and the most practical way 

of containing the material in one area for future recovery. The drums are starting 

to deteriorate and if one of the alternatives necessitating drum handling is 

selected, the abuse from the barrel rotator could create punctures, promote 

dusting, thus environmental problems. [Wright 1979] 

Sources show that in late 1987, a plan was implemented to repackage thorium materials 

contained in the Plant 8 silo and two thorium storage bins that were identified as having 

questionable structural integrity (Clark et al. 1989). A 1985 document (Mengel 1985) contains 

six BZ air sampling results for [redacted] workers involved in thorium redrumming. 

Importantly, Mengel 1985 states that all [redacted] workers involved in that particular 

redrumming operation wore respiratory protection; the document notes that time-weighted BZ 

samples indicate that levels were below the DOE limit for “soluble” thorium.7

 

It is clear that there were concerns over the integrity of thorium containers throughout the period 

of interest. SC&A’s interviews of workers has indicated that the respiratory protection was not 

always used when required, even, for instance, by chemical operators. Indeed, available 

documentation indicates that the use of respirators may not have provided consistent protection 

or any protection at all, at least up to 1980, since there were no procedures to ensure that 

respirators were being cleaned prior to reuse (Leist 1980). But, as noted above, there is also 

evidence that respiratory protection was used in mid-1985. This improved industrial hygiene 

situation should be viewed in the context of the DOE headquarters site-wide safety inspection of 

Fernald in February 1985. Furthermore, SC&A worker interviews also indicate that there were 

changes in regard to worker protection practices starting with the new contractor in 1986 (SC&A 

2006, Attachment 4, and Section 3.5 below). Evidence of poor industrial hygiene conditions 

prior to 1985 is provided below in Section 3.5. Hence, the evidence for 1985 of respirator use 

during a redrumming operation and the resulting relatively low intakes cannot be backextrapolated prior to 1985. NIOSH does not assume respirator use in its dose reconstruction 

(SC&A 2006, Attachment 2); SC&A is in agreement with this assumption. 

There are no systematic data on whether the workers who were involved in redrumming 

activities were adequately monitored for potential thorium intakes, or even whether they were 

monitored with any consistency at all during the decades of periodic redrumming operations. 

 6

 Item 1 stipulates that the drummed material be buried with the “contents intact;” however, documentation 

describing the actual operation could not be located. 

Draft Review – Proposed Attachment 32 June 28, 2010 

7

 The term “soluble” is used in Mengel 1985. Currently, only Types M and S are recognized for thorium 

compounds. The DOE limit was 66 dpm/m3

 for “soluble thorium in a controlled area” (Mengel 1985). 

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Health for factual accuracy or applicability within the requirements of 42 CFR 82.
Since the badge numbers for the [redacted] workers who were involved in the [redacted] 

redrumming operation are available (Mengel 1985), SC&A checked the NIOSH in-vivo data 

compilation for their thorium-232 records. [Redacted] of the [redacted] had in-vivo data in 

[redacted] (below the detection limit) and [redacted] had no data in [redacted] (though there 

was one result in [redacted] below the detection limit). This should not be a surprise, in view of 

their use of respirators with radionuclide filter cartridges in a post-headquarters-inspection work 

environment. Time-weighted air concentrations during the [redacted] redrumming were 

measured and were below the maximum allowable concentration. 

It is possible that some of the higher intakes for monitored workers in non-thorium areas may 

have been associated with redrumming operations, but this cannot be established with the 

available data. The redrumming workers who had these episodic exposures have not been 

identified, other than the [redacted] workers during a single redrumming operation in 

[redacted] discussed above. 

Given the lack of identification of redrumming workers and the associated in-vivo data, the 

relative exposure potential of redrumming workers either to thorium production workers or to all 

monitored workers cannot be established with the data available at present. In particular, the 

results for the [redacted] redrumming workers cannot be back-extrapolated. As noted above, 

SC&A has not investigated whether redrumming operations were systematically noted in 

logbooks along with measurements. None of the [redacted] workers identified in the [redacted] 

document has a job description in the coworker database indicating redrumming as an 

occupation of activity. The ORAUT white paper (ORAUT 2008) does not address the 

redrumming issue. 

The redrumming issue is also important to assessing the feasibility of a coworker model, because 

exposures were episodic and, at least in some cases prior to 1985, likely to have been high, as 

indicated by the pre-1985 documents quoted above. The NIOSH assumption that exposures 

occurred at the mid-point of the period between samples (ORAUT 2008, p. 11) would also 

inappropriate for such episodic exposures. (Also see Section 3.5 below.) 

3.4 FEASIBILITY OF IDENTIFYING ADDITIONAL THORIUM WORKERS 

As noted in Section 3.1, two main resources were identified that listed thorium workers; the 

Starkey memo (1968) and a compilation of in-vivo logbook sheets that had ‘thorium worker’ and 

‘former thorium worker’ handwritten on the top of the record. A major limitation of the Starkey 

memo is that it only identifies those thorium workers at the end of 1967 (likely for 1968 

campaigns), and does not indicate how long these workers handled thorium after this period. 

A search of available records for Fernald in the SRDB was undertaken to see if additional 

documentation exists that identifies the workers who handled thorium during later years. No 

evidence was found in this query to suggest that the documentation exists to identify additional 

workers who were involved in thorium production campaigns or who handled thorium materials. 

Draft Review – Proposed Attachment 33 June 28, 2010 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.
As stated in Section 3.3, a document was found that listed the names of [redacted] workers 

involved in a thorium redrumming operation in [redacted]; however, such documentation of 

workers involved in redrumming appears to be the exception rather than the rule. Another 

document from late August 1989 identifies workers who are to be trained in the thorium 

overpacking process (Westinghouse 1989); however, no such documentation could be identified 

for earlier periods to identify specific workers. At this time, SC&A has not found sufficient 

documentation or evidence that thorium workers can be identified for the years of interest, with 

the partial exception of 1968 (from the Starkey memo) and the 26 workers identified via 

production period in-vivo logsheets. 

3.5 POTENTIAL INADVERTENT EXPOSURE TO NON-THORIUM WORKERS 

Documentation suggests several problems arising from thorium operations that may have created 

an exposure potential to workers in the vicinity, but not directly involved in thorium activities. A 

document from 1970 notes significant industrial hygiene problems related to thorium metal 

production: 

Probably the worst housekeeping problem in the facility is the Ball Mill. This 

equipment leaks excessively at practically every joint. All horizontal surfaces 

have a thick covering of dust. In operation, this dust becomes airborne and adds 

to the dust coming from the leaks. Since the ventilation is inadequate and there is 

no proper enclosure, a bucket was placed under the largest leak to help contain 

the spilled dust... During the operation of removing the calcined ThF4 and CaF2

from the retorts, the stack of trays is left standing on a skid near the south annex 

door. The door is left open to aid in cooling the trays. The wind coming through 

the door blows the loose powder from the trays and spreads it generously through 

the annex. Removing the trays from the support requires heavy effort and this 

dislodges more powder to be spread by the wind... In every inspection, it has 

been noticed that thorium containing material was spilled in many locations. 

[Ross 1970] 

The problems associated with health and safety practices, such as excessive dust and disregard 

for safety procedures, were documented in 1980 during a week-long appraisal of the FMPC 

health protection program conducted by Oak Ridge Office (ORO). The results of this health and 

safety review are summarized in Leist 1980. The review identified several instances of workers 

in dusty areas not utilizing proper ventilation or respirators. Specifically, the appraisal stated the 

following conclusions: 

- ... there were basic defects in our health and safety concepts. Further, that 

they had noted willful disregard of NLO regulations for health and safety and 

would conclude that management is not committed to this end. 

- NLO should retrain on the use of respirators...NLO has no respirator 

recycling check procedures to insure they are being cleaned properly. 

Draft Review – Proposed Attachment 34 June 28, 2010 

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- NLO has no routine area radiation monitoring plan and we should institute 

one... NLO’s air monitoring program is minimal and should be expanded to 

avoid exposures. 

- The appraisers found a basic lack of concern for spills clean-up and longer 

term exposure in the plants and a lack of reflection of Management’s concern 

in this area with the line people. The appraisers also feel that our safety 

programs are not being implemented. [Leist 1980]

Thorium production campaigns ended in 1979, so are not directly covered by this health physics 

appraisal; however, it cannot be assumed a priori that conditions were better in the earlier period 

without direct evidence. Later in the 1980s, the air monitoring program was characterized as 

follows: 

When WMCO began administration of the DOE contract for operation of the 

Feed Materials Production Center in January of 1986, the FMPC air sampling 

program was very limited. WMCO has aggressively upgraded the air sampling 

program by providing written procedures, introducing continuous sampling, 

posting all ‘Airborne Radioactivity Areas’ at 10 percent of the established limit, 

setting up Beta and Alpha CAMs to provide real time monitoring, requiring 

respiratory protection in all ‘Airborne Radioactivity Areas’ and providing 

continuous radon/thoron working level monitoring. (Rogers 1989) 

Given the industrial hygiene problems documented in 1980 and the air monitoring program that, 

as late as 1986, was described as “limited,” it is possible that workers passing through thorium 

areas were exposed to contaminated dusts that may or may not have been monitored for thorium 

during the period of interest (1968–1989). It is not clear to what extent these potential exposures 

might be covered by the in-vivo program. 

Draft Review – Proposed Attachment 35 June 28, 2010 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.
REFERENCES 

Clark, T.R., L. Elikan, C.A. Hill, and B.L. Speicher 1989. “History of FMPC Radionuclide 

Discharges – Revised Estimates of Uranium and Thorium Air Emissions from 1951–1987,” 

Addendum to FMPC-2082. Westinghouse Materials Company of Ohio, March 1989. SRDB 

Ref ID: 2495. 

Defazio, P.G. 1965. “Ventilation for Redrumming of Thorium Residues.” National Lead 

Company of Ohio, November 17, 1965. SRDB Ref ID: 28944. 

Leist, N.R. 1980. Minutes of Close-Out Meeting Health Physics – Industrial Hygiene Appraisal. 

National Lead Company of Ohio, October 10, 1980. SRDB Ref ID: 4193. 

Lucas, H.F. and A.F. Stehney 1988. “228Th and 232Th in tissue from exposed persons.” 

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Mengel, W.H. 1985. “BZ Alpha Concentrations during Building 65 Thorium Redrumming.” 

National Lead Company of Ohio, June 25, 1985. SRDB Ref ID: 34321. 

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42940. 

Neblett, F.W. 1972. Meeting Minutes – Thorium Residue Management. National Lead of Ohio, 

April 25, 1972. SRDB Ref ID: 28926. 

NRPB 2004. G.N. Stradling, A. Hodgson, T.P. Fell, A.W. Phipps, and G. Etherington, Thorium 

Nitrate and Dioxide: Exposure Limits and Assessment of Intake and Dose after Inhalation, 

NPRB-W57 National Radiological Protection Board, Oxon (UK), 2004. 

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(FEMP) – Occupational Internal Dose, ORAUT-TKBS-0017-5, Rev. 0, Oak Ridge Associated 

Universities Team, Cincinnati, Ohio. May 28, 2004 

ORAUT 2005. Technical Information Bulletin: Analysis of Coworker Bioassay Data for 

Internal Dose Assignment, ORAUT-OTIB-0019, Rev. 01, Oak Ridge Associated Universities 

Team, Cincinnati, Ohio. October 7, 2005. 

ORAUT 2006. Procedure: Generating Summary Statistics for Coworker Bioassay Data, 

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Draft Review – Proposed Attachment 36 June 28, 2010 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.
Draft Review – Proposed Attachment 37 June 28, 2010 

 This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

NOTICE:

ORAUT 2008. “Thorium In Vivo Coworker Study for FEMP – A Proposed Attachment for 

ORAUT-TKBS-0017-5,” Rev. 1, Oak Ridge Associated Universities Team, Cincinnati, Ohio. 

January 8, 2008. 

Rogers, R.M. 1989. “Radiological Air Sampling Program and Air Sampling Philosophy.” Feed 

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4152. 

Ross, K.N. 1970. “Thorium Metal Production Housekeeping.” National Lead Company of 

Ohio, June 8, 1970. 

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Project (Feed Materials Production Center), S. Cohen & Associates, Vienna, Virginia. 

Starkey, R.H. 1967. “Thorium Workers.” National Lead Company of Ohio. December 26, 

1967. SRDB Ref ID: 43069. 

Starkey, R.H. 1968. “Problems Associated with Thorium Processing – Plant 8.” National Lead 

Company of Ohio, October 1, 1968. 

Stehney, A.F. and H.F. Lucas 2000. “Thorium isotopes in autopsy samples from thorium 

workers.” Health Phys. 78:8-14. 

Stradling, N., A. Phipps, and A. Hodgson 2001. “Dosimetric models for thorium and practical 

problems in assessing intakes.” Radiat. Prot. Dosim. 97:89-94. 

Union Carbide 1979. Mobile Counter Sensitivities, Union Carbide Nuclear Division Internal 

Correspondence, January 24, 1979. SRDB Ref. ID 32630. 

Westinghouse 1989. Attendance Roster: Systems Operations (Thorium metals Overpacking 

Process). Westinghouse Training – Human Resources Department. August 21, 1989. SRDB 

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Wright, W.W. 1979. “Removal of Thorium Residues from Inventory – FY 1980.” National 

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